Currently, connections between telecommunications cards in routers are realised via a backplane based on electrical circuitry. The backplane comprises electrical lines and, at the interfaces between the backplane and each of the cards the backplane comprises an electrical pin. The cards are plugged onto the electrical pins. Usually the cards can be plugged onto the pins without the need for a mechanical adjustment mechanism, although an exception exists for particularly dense cards, where a mechanical adjustment mechanism might be required to increase the insertion accuracy, so as to avoid damaging the pins.
However, as data throughput continues to increase, these electrical connections will need to be updated to support higher capacity. The next throughput capacity will require line cards to process data flows at 400 Gbps and beyond. Thus, the electrical lines will be required to support increased electrical bandwidth, for example up to 25 GHz over tens of centimeters.
At these distances and capacities using optical rather than electrical lines to realise the connections is a viable alternative, due to the ability of optical connections to support high throughput, with a more sustainable footprint, lower power consumption, interference and density.
In the article “An optical Backplane Connection System with Pluggable Active Board Interfaces”, Richard Pitwon, Ken Hopkins and Dave Milward, Xyratex White Paper 2007 a system is proposed for providing optical connections between line cards in a router.
However, a problem with this system is that the tolerance to lateral misalignment of the optical interfaces is only in the region of 50 micrometers. In comparison, the tolerance to lateral misalignment for electrical pins is approximately 1 millimeter. Thus, mechanical mechanisms are required to align the transmitting and receiving optical interfaces, in order to achieve good system performance and avoid wasting optical power. However, these mechanisms are costly, as they need to compensate for vibrations, temperature changes and ageing, and there are also operational costs involved to train personnel at the sites to operate the mechanisms. Further, active self-aligning mechanisms for the optical interfaces are also unpractical, for cost, reliability, life time and power consumption reasons.
The present invention aims to address these problems.